I think you're on the right track with English - keep learning it and try to spend one or two years in an English-speaking country during your studies. You can make a living with a straight FR-EN A-B combination.

If you want to learn other languages then, at the same time you could continue learning 1 other language, RU is harder but probably more likely to make you employable than ES. FR EN ES is a common combination, yes. And if you can try to get a year in a country where that language is spoken as well. You might get it up to a C by then.
(If you want to work for the EU you will need DE and another EU language)

But importantly do languages you like in countries you like, because there is no guarantee that in 5 years time you will still want to be an interpreter, nor that you are actually cut out for interpreting. All of that will become clear in the course of time.